1. Field of the Invention
This invention relates generally to composite articles. More specifically, the invention relates to a method of producing molded board products useful for packaging components.
2. Description of Related Technology
Many types of wood composites exist, including, for example: fiberboards such as hardboard, medium density fiberboard, and softboard; chipboards such as particleboard, waferboard; and oriented strandboard. Boards made of combinations of these materials are also useful.
Many different methods of manufacturing these wood composites such as fiberboard are known in the art, for example as disclosed in U.S. Pat. No. 4,514,532 (Apr. 30, 1985) to Hsu et al. and U.S. Pat. No. 4,828,643 (May 9, 1989) to Newman et al. The disclosures of these patents are incorporated herein by reference. The principal processes for the manufacture of fiberboard include (a) wet felted/wet pressed or xe2x80x9cwetxe2x80x9d processes, (b) dry felted/dry pressed or xe2x80x9cdryxe2x80x9d processes, and (c) wet felted/dry pressed or xe2x80x9cwet-dryxe2x80x9d processes. Synthetic resins, such as phenol-formaldehyde (xe2x80x9cPFxe2x80x9d) resins or modified PF resins, are often used as binders in these processes.
Generally, in a wet process, cellulosic fibers (e.g., woody chip material subjected to fiberization in a pressurized refiner to form wood fibers) are blended in a vessel with large amounts of water to form a slurry. The slurry preferably has sufficient water content to suspend a majority of the wood fibers and preferably has a water content of at least 95 percent by weight (xe2x80x9cweight percentxe2x80x9d). The water is used to distribute a synthetic resin binder, such as a phenol-formaldehyde resin over the wood fibers. This mixture is deposited onto a water-previous support member, such as a fine screen or a Fourdrinier wire, and precompressed, whereby much of the water is removed to leave a wet mat of cellulosic material having, for example, a moisture content of about fifty percent, based on the weight of dry cellulosic material. The wet mat is transferred to a press and consolidated under heat and pressure to form the molded wood composite.
A wet-dry forming process can also be used to produce wood composites. Preferably, a wet-dry process begins by blending cellulosic material (e.g., wood fiber) in a vessel with a large amount of water. This slurry is then blended with a resin binder. The blend is then deposited onto a water-pervious support member, where a large percentage (e.g., 50 weight percent or more) of the water is removed, thereby leaving a wet mat of cellulosic material having a water content of about 40 wt. % to about 60 wt. %, for example. This wet mat is then transferred to a zone where much of the remaining water is removed by evaporation by heat to form a dried mat. The dried mat preferably has a moisture content of about 10 wt. % or less. The dried mat is then transferred to a press and consolidated under heat and pressure to form a wood composite which may be a flat board or a molded product, for example. The product can be molded into various shapes or geometries depending on the intended use.
In a dry process, the wood fibers are generally conveyed in an airstream or by mechanical means, rather than by a liquid stream. Wood fibers supplied from a fiberizing apparatus are blended with a thermosetting resin binder, such as a phenol-formaldehyde resin, and a sizing agent such as wax. The fibers with an addition of resin (3-10%) and wax can be dried and then be randomly formed into a mat (felted) by air blowing the fibers onto a support member. The mat, typically having a moisture content of about 5-8 wt. % based on the weight of dry fibers, is then pressed under heat and pressure to cure the thermosetting resin and to compress the mat into an integral consolidated structure. This mat can be pressed into various shapes varying from flat panel to three-dimensional using machined die sets.
When pressing mats into a ribbed configuration, however, various problems may arise. When creating ribbed high density fiberboard, fracturing of the board can occur at the flats of the ribbed configuration, reducing the strength and handleability of the product. Other problems may include a soft surface, lack of consolidation, brittleness, blistering, and warping in the final product.
It would therefore be desirable to be able to manufacture a ribbed high density fiberboard that does not fracture during manufacturing.
The present application is also directed to the production of packaging components such as pallets. Pallets are currently made from a variety of different materials such as wood, plywood, wood composites, plastic, corrugated cardboard, and metal. These materials each have their own distinct advantages and disadvantages. Solid wood remains the most common material used in pallets because of its low cost and high strength and stiffness. Wood, however, has inconsistent composition, is heavy when wet, and requires a great deal of labor when assembling into pallets.
Plywood pallets are known for their long life expectancy of seven to eight years. In addition, plywood pallets are easy to repair. However, plywood can be heavy. Furthermore, it may be more expensive, because it must be cut from a four foot by eight foot panels, which causes a lower yield per panel.
Plastic pallets, including those made of high density polyethylene, have also been used. However, they can be four times more expensive than wood pallets. Advantages of plastic pallets are moldability and cleanability. Sag resistance, fire threats, and difficult repairability are known limiting factors.
Metal pallets are used by the smallest segment of the industry. They are very expensive, but they can hold large loads and they are virtually indestructible.
Wood/plastic composite pallets, such as those available from Dura Products International of Toronto, Ontario and Litco International Inc. of Vienna, Ohio can be made from sawdust shavings and waste plastic bottles. Wood composite pallets are lighter than wood, fully recyclable, economically competitive, and have consistent dimensions. The weaknesses of composite pallet products include rackability, which is limited to 2800 pounds. Further, if some types of wood/plastic composite products are exposed to fire, they can emit toxic fumes.
Corrugated cardboard pallets are single-use items, and are limited to a 500 to 2,800 pound weight limit. The advantages of corrugated material include recyclability and design flexibility. These pallets are safe for the worker to handle, are easy to dispose of, produce no splinters, use no nails, have product uniformity free of mold spores, and are one-third the weight of wood. However, corrugated pallets are more easily damaged than wood, difficult to use on conveyor systems, weight restricted, and will degrade in the presence of water. Corrugated pallets can be wax coated so as to delay water damage. However, when such products are wax coated, they become more expensive and difficult to recycle.
It would therefore be desirable to manufacture a pallet that retains the beneficial properties of corrugated pallets while increasing its water resistance and strength attributes.
It is an object of the invention to overcome at least one of the problems described above.
According to the invention, a mat including material such as wood-based materials, agricultural fibers, and synthetic fibers and a binder resin is provided in a die configured to produce a ribbed composite board having contiguous outer zones and angled zones. The die is configured to produce a caliper difference between the outer zones and the angled zones, preferably wherein the outer zones have a caliper less than the angled zones.
According to an embodiment of the invention a component, such as a deck or strips, incorporates the ribbed composite board of the invention.
Other objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the drawings and the appended claims.